1. Field of the Invention
The present invention relates to an alloy intended to be used in the manufacture of centrifuges. This alloy is particularly suitable for constructing centrifuges which produce glass fibers.
2. Description of the Background
A centrifuge of this type rotates about its vertical axis at a velocity of the order of 800 to 4000 rpm. A large number of apertures are provided on its peripheral wall. An annular combustion chamber adjacent the centrifuge produces a descending gaseous current which passes along the peripheral wall of the centrifuge and draws the thin streams of glass emerging from the apertures in order to produce small glass fibers.
Molten glass is introduced into the centrifuge and is sprayed under the action of centrifugal force towards the inner face of the peripheral wall of the centrifuge. The molten glass passes through the apertures in this wall. The thin glass streams produced outside the centrifuge are then drawn out by the action of the gaseous current.
The stresses to which the centrifuge is subject are threefold: thermal shocks on stopping and starting, hot flow because of the centrifugal forces, and corrosion of the fibre drawing apertures by the glass. As an example, the operating temperatures are of the order of 1000.degree.-1200.degree. C. These are the temperatures at which the glass is at a suitable viscosity.
In view of the particularly harsh operating conditions, centrifuges deteriorate when used for a relatively long time. These centrifuges may have to be replaced for various reasons which include deformation of the fibre-drawing strip, the appearance of horizontal or vertical cracks, large scale wear of the apertures, and the like.
In practice, the most frequent reasons for changing centrifuges are still deformation of the peripheral strip which is manifested by a deterioration in the quality of the fibers produced. This deformation is connected both with the effects of centrifuging on the peripheral strip and weakening of the latter by erosion of the apertures. Nevertheless, an improvement in resistance to corrosion and to deformation cannot be separated from questions concerning the fragile nature of the alloy. It is particularly important to avoid rupture of the centrifuges during operation. It is therefore necessary to select the centrifuge alloy such that it has good resistance to deformation, on the one hand, and, on the other hand, that it is not too fragile. Since these two features are at least on part contradictory, a compromise solution must be reached.
Ni and Cr based alloys for constructing centrifuges of this type are known, in particular, as disclosed in French Patent 2,459,783. This patent recommends an alloy composition which is relatively precise with regard to its principal constituents, in particular the carbon content. Centrifuges produced from the alloy of the prior art on the whole display improved properties. Overall these centrifuges have satisfactorily useful lives. Nevertheless, some centrifuges among those complying with the features of this disclosure have useful lives which are far shorter than the average useful life without any possible explanation for this, and thus any means of foreseeing the reasons for these incidents.
In view of this situation, a need has continued to exist for a solution which enables centrifuges to have the desired useful lives so that they may experience a consistent demand for production.